JDBC（一）

1.   JDBC介绍

JDBC(Java DataBase Connectivity)，即Java数据库的连接。JDBC是一种用于执行SQL语句(DML,DDL,DQL)的Java API，可以为多种关系数据库（oracle,mysql,sqlserver）提供统一访问，它由一组用Java语言编写的类和接口组成。JDBC提供了一种基准，据此可以构建更高级的工具和接口，使数据库开发人员能够编写数据库应用程序。

Java 通过JDBC访问数据库，数据库厂家有很多，如Mysql、Oracle、SqlServer等，而JDBC提供了操作这些数据库的统一的接口、基准，让各大厂商去实现这组规范。各大数据库厂商只需要提供对应的JDBC的jar包，使java代码通过不同厂商实现的jar包访问对应的数据库。

2.   JDBC完成CRUD规范步骤

2.1.规范DAO层的实现

DAO层：涉及到开发中的三层架构与MVC层级结构。DAO层叫数据访问层，全称data access object，属于一种比较底层、比较基础的操作，具体作用于某个表、某个实体的增删改查。

DAO层的创建规范：

这里包括界面层传入数据封装成为的域对象——Domain类对象。

2.2. DAO层具体实现

具体代码如下：

DAO层：

接口：

 public interface IStudentDao {

     public void insert(Student student);

     public void update(Student student);

     public void delete(Integer id);

     public Student queryOne(Integer id);

     public List<Student> queryAll();
 }

实现类Impl：

 package cn.yif.dao.impl;

 import cn.yif.domain.Student;
 import cn.yif.dao.IStudentDao;
 import cn.yif.utils.JDBCUtil;

 import java.sql.*;
 import java.util.ArrayList;
 import java.util.List;

 /**
  * @author Administrator
  * @create 2019-09-13-20:33
  */
 public class StudentDaoImpl implements IStudentDao {
     @Override
     public void insert(Student student) {
         Connection conn = null;
         Statement statement = null;
         try {
             //①加载（注册）驱动，这部分硬编码可以写也可以不写，jdbc4.0版本自带了
             //Class.forName("com.mysql.jdbc.Driver");
             //②获取连接
             //conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/jdbctest01", "root", "admin");
             conn = JDBCUtil.getInstance().getConnection();
             //③获取语句对象：用来执行SQL语句
             statement = conn.createStatement();
             //④执行SQL语句
             String insertSql = "insert into jdbcdemo01 (name, age) values ('"+student.getName()+"', "+student.getAge()+")";
             statement.execute(insertSql);
         }catch (Exception ex){
             ex.printStackTrace();
         }finally {
             //⑤释放资源
             JDBCUtil.getInstance().close(null, statement, conn);
         }
     }

     @Override
     public void update(Student student) {
         Connection conn = null;
         Statement statement = null;
         try {
             //①加载（注册）驱动
             //Class.forName("com.mysql.jdbc.Driver");
             //②获取连接
             //conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/jdbctest01", "root", "admin");
             conn = JDBCUtil.getInstance().getConnection();
             //③获取语句对象：用来执行SQL语句
             statement = conn.createStatement();
             //④执行SQL语句
             String updateSql = "update jdbcdemo01 set name = '"+student.getName()+"', age = "+student.getAge()+" where id = "+student.getId()+"";
             statement.execute(updateSql);
         }catch (Exception ex){
             ex.printStackTrace();
         }finally {
             //⑤释放资源
             JDBCUtil.getInstance().close(null, statement, conn);
         }
     }

     @Override
     public void delete(Integer id) {
         Connection conn = null;
         Statement statement = null;
         try {
             //①加载（注册）驱动
             //Class.forName("com.mysql.jdbc.Driver");
             //②获取连接
             //conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/jdbctest01", "root", "admin");
             conn = JDBCUtil.getInstance().getConnection();
             //③获取语句对象：用来执行SQL语句
             statement = conn.createStatement();
             //④执行SQL语句
             String deleteSql = "delete from jdbcdemo01 where id = "+ id +"";
             statement.execute(deleteSql);
         }catch (Exception ex){
             ex.printStackTrace();
         }finally {
             //⑤释放资源
             JDBCUtil.getInstance().close(null, statement, conn);
         }
     }

     @Override
     public Student queryOne(Integer id) {
         Connection conn = null;
         Statement statement = null;
         ResultSet resultSet = null;
         Student student = null;
         try {
             //①加载（注册）驱动
             //Class.forName("com.mysql.jdbc.Driver");
             //②获取连接
             //conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/jdbctest01", "root", "admin");
             conn = JDBCUtil.getInstance().getConnection();
             //③获取语句对象：用来执行SQL语句
             statement = conn.createStatement();
             //④执行SQL语句
             String queryOneSql = "select * from jdbcdemo01 where id = "+ id +"";
             resultSet = statement.executeQuery(queryOneSql);
             if(resultSet.next())
             {
                 student = new Student();
                 student.setId(resultSet.getInt("id"));
                 student.setName(resultSet.getString("name"));
                 student.setAge(resultSet.getInt("age"));
             }
         }catch (Exception ex){

         }finally {
             //⑤释放资源
             JDBCUtil.getInstance().close(resultSet, statement, conn);
         }
         return student;
     }

     @Override
     public List<Student> queryAll() {
         Connection conn = null;
         Statement statement = null;
         ResultSet resultSet = null;
         Student student = null;
         List<Student> list = new ArrayList<Student>();
         try {
             //①加载（注册）驱动
             //Class.forName("com.mysql.jdbc.Driver");
             //②获取连接
             //conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/jdbctest01", "root", "admin");
             conn = JDBCUtil.getInstance().getConnection();
             //③获取语句对象：用来执行SQL语句
             statement = conn.createStatement();
             //④执行SQL语句
             String queryAllSql = "select * from jdbcdemo01";
             resultSet = statement.executeQuery(queryAllSql);
             while (resultSet.next())
             {
                 student = new Student();
                 student.setId(resultSet.getInt("id"));
                 student.setName(resultSet.getString("name"));
                 student.setAge(resultSet.getInt("age"));
                 list.add(student);
             }
         }catch (Exception ex){
             ex.printStackTrace();
         }finally {
             //⑤释放资源
             JDBCUtil.getInstance().close(resultSet, statement, conn);
         }
         return list;
     }
 }

Domain层：

 package cn.yif.domain;

 /**
  * @author Administrator
  * @create 2019-09-13-20:23
  */
 public class Student {
     //ID表示编号
     private Integer id;

     //name表示名字
     private String name;

     //age表示年龄
     private Integer age;

     public Integer getId() {
         return id;
     }

     public void setId(Integer id) {
         this.id = id;
     }

     public String getName() {
         return name;
     }

     public void setName(String name) {
         this.name = name;
     }

     public Integer getAge() {
         return age;
     }

     public void setAge(Integer age) {
         this.age = age;
     }

     public Student() {
     }

     public Student(Integer id, String name, Integer age) {
         this.id = id;
         this.name = name;
         this.age = age;
     }

     @Override
     public String toString() {
         return "Student{" +
                 "id=" + id +
                 ", name='" + name + '\'' +
                 ", age=" + age +
                 '}';
     }
 }

工具类JDBCUtil实现：

 package cn.yif.utils;

 import java.io.IOException;
 import java.sql.*;
 import java.util.Properties;

 /**
  * @author Administrator
  * @create 2019-09-13-21:21
  */
 public class JDBCUtil {
     //使用静态static类构造单例模式
     private JDBCUtil(){ }
     //在静态代码块中创建instance的实例，这里使用static静态变量来保存
     private static JDBCUtil instance = null;
     //每次都要加载驱动，这里定义一个Properties，把资源文件里面的内容读到Properties里面
     private static Properties properties = null;
     //JDBCUtil类加载的时候，就加载注册驱动
     static {
         properties = new Properties();
         try {
             //当前线程类加载器加载获取properties文件
             properties.load(Thread.currentThread().getContextClassLoader().getResourceAsStream("jdbc.properties"));
             try {
                 Class.forName(properties.getProperty("driverClassName"));
             } catch (ClassNotFoundException e) {
                 e.printStackTrace();
             }
         } catch (IOException e) {
             e.printStackTrace();
         }

         instance = new JDBCUtil();
     }

     public static JDBCUtil getInstance(){
         return instance;
     }

     //抽取获取连接Connection的方法
     public Connection getConnection() throws SQLException {
        return DriverManager.getConnection(properties.getProperty("url"), properties.getProperty("username"), properties.getProperty("password"));
     }

     //抽取JDBC关闭资源的close方法
     public void close(ResultSet resultSet, Statement statement, Connection conn){
         try {
             if(resultSet != null){
                 resultSet.close();
             }
         } catch (SQLException e) {
             e.printStackTrace();
         }
         try {
             if(statement != null){
                 statement.close();
             }
         } catch (SQLException e) {
             e.printStackTrace();
         }
         try {
             if(conn != null){
                 conn.close();
             }
         } catch (SQLException e) {
             e.printStackTrace();
         }
     }
 }

JDBC资源配置文件：

 driverClassName = com.mysql.jdbc.Driver
 url = jdbc:mysql://localhost:3306/jdbctest01
 username = root
 password = admin

或GitHub：https://github.com/devyf/JavaWorkSpace/tree/master/JDBC_0913_01